allow build to proceed if either Qt or QScintilla is missing * configure.ac: Instead of aborting the configure script, set build_gui to "no" if Qt is missing. Don't abort configure script if QScintilla is missing. If QScintilla is available, define HAVE_QSCINTILLA. * file-editor-tab.cc, file-editor.cc, find-dialog.cc, lexer-octave-gui.cc: Surround file contents with #ifdef HAVE_QSCINTILLA. * main-window.cc (main_window::~main_window): Skip deletion of _file_editor if HAVE_QSCINTILLA is not defined. (main_window::new_file, main_window::open_file, main_window::focus_editor): Do nothing if HAVE_QSCINTILLA is not defined. (main_window::handle_entered_debug_mode, main_window::handle_quit_debug_mode): Skip operation on _file_editor if HAVE_QSCINTILLA is not defined. (main_window::construct): Skip creation of _file_editor and operations on it if HAVE_QSCINTILLA is not defined. * main-window.h (main_window::_file_editor): Omit data member from class if HAVE_QSCINTILLA is not defined.

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debug/
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